Field of the Invention
The present invention relates to a projection optical system and a projection type display apparatus using the same.
Description of the Related Art
Recently, a projection type display apparatus that projects an image on a screen having convex or concave portions or a cylindrical curvature or on an object surface having a step has been increased to further enhance a realistic sensation. In a general projector, a projection lens is designed such that its image surface becomes substantially flat to focus on the entire flat screen.
Therefore, in the case where an image is projected on a surface which is not flat such as a screen having a curvature, a focus can be put on the specific position such as the center of the screen similar to the case where an image is projected on a flat surface. However, the other positions are out of focus due to difference of a distance from the flat surface.
As a technique for solving the problem described above, projection lenses discussed in Japanese Patent Application Laid-Open No. 3-196009 and Japanese Patent Application Laid-Open No. 2011-145580 have been known. According to Japanese Patent Application Laid-Open No. 3-196009 and Japanese Patent Application Laid-Open No. 2011-145580, a lens unit is moved according to the average curvature of a screen to purposefully produce field curvature, by which the entire projected image is focused, similar to an image projected on a flat screen, even when an image is projected on a curved screen.
In the case where field curvature adjustment is performed by moving the lens unit as discussed in Japanese Patent Application Laid-Open No. 3-196009 and Japanese Patent Application Laid-Open No. 2011-145580, the phenomenon described below may occur.
That is, depending on the lens unit which is moved to perform the field curvature adjustment, an angle of view is changed due to the movement of the lens unit, which may possibly change the size of the projected image. To address this phenomenon, Japanese Patent Application Laid-Open No. 2011-145580 discusses a technique for adjusting the position of each lens unit through the field curvature adjustment to cancel the change in the angle of view caused by the field curvature adjustment.
However, Japanese Patent Application Laid-Open No. 2011-145580 does not discuss a method for reducing the effect itself produced on the projected image as a result of the field curvature adjustment, such as the change in the angle of view described above.